The small GTPase Ras relays signals from activated cell surface receptors to intracellular signaling pathways. In adenocarcinomas, which originate from polarized epithelial cells, Ras signaling is often deregulated as a result of activating mutations or gene amplification. The mechanisms by which oncogenic Ras elicits transformation of polarized epithelial cells are poorly understood. A major effector pathway of Ras signaling is the Raf-MEK-ERK pathway, which mimics numerous effects of Ras on cells. Expression of activated Ras or Raf in polarized epithelial cells leads to profound alterations in the actin cytoskeleton and associated changes in cellular architecture. The actin eytoskeleton is subject to control by Rho family GTP-binding proteins. Ras or Raf activation in polarized epithelial cells leads to induced expression of the Rho-like protein Rnd3, which appears to function as an endogenous antagonist to Rho proteins. Accordingly, effects of Rnd proteins on cells are counteracted by expression of activated forms of Rho proteins. Virtually nothing is known about effector molecules of Rnd signaling. It is important to identify effectors of Rnd proteins as their expression in cells elicits a phenotype that suggests that they play key roles in cell transformation and developmental processes. In new studies we have identified the Rho GTPase activating protein p190 as a putative effector molecule of Rnd signaling. Aim 1 is to dissect the interaction between Rnd and p190 proteins and to generate an inhibitory molecule of this interaction. Aim 2 is to test the hypothesis that the interaction between Rnd and p190 molecules affects functional domains of the p190 molecule, and that p190 is an effector molecule of Rnd proteins in vivo using cells in which p190 has been knocked out. Aim 3 addresses whether the Rnd-p190 interaction is critical to oncogenic transformation of polarized epithelial by the Ras activated Raf-MEK-ERK pathway using the inhibitory molecule generated in Aim 1. Together, the proposed studies will elucidate mechanisms whereby Ras transforms epithelial cells leading to invasion and metastasis.